Aims: Phenolphthalein, a constituent in many laxatives, showed clear evidence of carcinogenic activity in 2-year feeding studies in rodents recently completed by the National Toxicology Program (NTP). About 3% of the older U.S. population uses phenolphthalein-containing laxatives on a daily basis. We will investigate the relation of phenolphthalein-containing laxative use with risk of ovarian cancer and adenomatous colorectal polyps in humans. Accomplishments: We established collaborative agreements with the principal investigators for two case-control studies of risk factors for ovarian cancer. At our instigation, these investigators inserted into their questionnaire a 2-page addition that ascertains use of specific phenolphthalein-containing laxatives. A report from the first such study was published and data from the remaining study (300 cases and 300 controls) will be ready for analysis in 2001. The published report shows no association of phenolphthalein-containing laxative use and risk of ovarian cancer. Data on laxative use were available to us from two case-control studies of risk factors for adenomatous colorectal polyps. We examined laxative use in relation to risk of polyps in these data. The association of polyps with use of all laxatives and phenolphthalein-containing laxatives was specifically explored after taking into account dietary and other risk factors for colorectal adenomas. Results from the two studies were inconsistent with each other but overall offered little support for an association between phenolphthalein-containing laxative use and risk of polyps. The report was published in 1997.